Abstract:The Flügge curved beam was applied to approximate the curved pipe to obtain the dynamic equations of in-plane vibration of curved pipe conveying fluid based on total inextensible assumption and the fluid acceleration was also deduced. After establishing the wave propagation and reflection matrices, the wave propagation method for calculating the natural frequency of curved pipe’s in-plane vibration was proposed. In the example, the critical velocity of a semi-circular pipe with clamped support at both ends was calculated. The result was compared with that in existing literature and great agreement was shown. Finally, the first four natural frequencies of clamped-clamped semi-circular pipe conveying fluid were obtained in six different cases of fluid velocity. The results shown that the increasing fluid velocity can make the natural frequencies of pipe decreased and when the fluid velocity increased to a certain value, the first natural frequency vanished.